Photoelectric conversion devices are employed for devices such as image sensors and X-ray image detectors. Especially, an X-ray image detector employing a flat panel such as the PD array substrate is called as a flat-panel X-ray detector (also called as a Flat Panel Detector, which is referred as a FPD hereinafter). Corresponding to the recent spread of digitization of image signals, the replacement of conventional analog films by FPDs for static images is advancing in the field of photographic devices, and the replacement of IIs (Image Intensifiers) by FPDs for moving images is advancing in the field of fluoroscopic devices. Therefore, FPDs are important devices in the field of medical image diagnostic apparatuses.
FPDs are divided in devices of a direct conversion type and devices of an indirect conversion type by their method of converting X-rays to electric charges. The devices of the direct conversion type use a conversion layer made of a material such as selenium (Se) to convert X-rays directly into charges. The devices of the indirect conversion type use a scintillator made of a material such as cesium iodide (CsI) and mounted on the above-described PD array substrate, to convert X-rays into visible rays with the scintillator and successively to perform a photoelectric conversion with PDs. The indirect conversion type exhibits a higher S/N ratio and can take images with a low-dose X-ray irradiation in comparison with the direct conversion type. Therefore, many FPDs of the indirect conversion type are being developed because they can achieve a reduction of levels of patient exposure. Especially, PDs with higher sensitivity are required in order to realize a much more reduction of patient exposure, for fluoroscopic devices.
The following characteristics are required for PD devices with high sensitivity: “high quantum efficiency” so as to achieve an effective photoelectric conversion though the amount of photons is extremely small; “low dark current” so as to keep a small amount of electrons after the conversion; and “small diode capacity” so as to restrict image lag and realize high-speed responsibility. These characteristics can be realized by increasing the thickness of a photoelectric conversion layer. However, the increased thickness of a photoelectric conversion layer can cause a layer separation in the manufacturing process, concretely, in the step of forming the layer and the succeeding steps, which has been a problem.
The main factor causing the problem is a membrane stress coming from the shrinkage difference among layers constituting the device, which is caused because of a temperature change from a high temperature state to a room temperature in the layering process. By lowering the layering temperature, the primary part of the shrinkage can be reduced and the layer separation to be generated in the whole part of the substrate can be solved, which can be easily imagined. However, it hardly solves a local layer separation which is caused when a difference in layer shrinkage is caused locally, for example, at the border of a patterned structure formed on the base, and membrane stress concentrates at the point. Further, it means that the layering temperature which is important as a factor to control the membrane properties of the photoelectric conversion layer, is restricted. Therefore, a structure not to cause a layer separation therein is required also for the purpose to enlarge the controllability of the membrane properties.
Various technologies to solve the layer separation have been conventionally proposed. Japanese Unexamined Patent Application Publications (JP-A) Nos. 2009-147203 and 2004-063660 disclose the structure that, in view of the layer separation of the photoelectric conversion layer caused because a photoelectric conversion layer made of amorphous silicon and its base are not tightly coupled together, at least a base on which an isolated pattern of the photoelectric conversion layer does not include a layer made of silicon nitride.
However, especially when a thick photoelectric conversion layer is formed, the layer can greatly shrink in its layering and processing steps. Therefore, the difference in adhesion properties between an area where the base includes a silicon nitride film and an area where the base does not includes a silicon nitride film, and the difference in line expansion coefficient between structures in the base have made concentration of stress coming from the layer shrinkage in the photoelectric conversion layer, on the boundary of different patterned structures on the base, which have resulted in the layer separation generated locally. As described above, the prior arts has failed to solve the layer separation and caused low production yield and contamination of the device so as to affect other substrates.
In view of that, JP-A Nos. 2009-147203 and 2010-067762 disclose the structure that, on layering and processing the photoelectric conversion layer, the whole of the base is formed by a lower electrode layer. Thereby, there are no parts to cause the concentration of stress in the base of the photoelectric conversion layer, which reduces the local layer separation.
However, in the prior arts, the lower electrode layer is formed by a patterning process after the photoelectric conversion layer is patterned, since the whole of the base in processing the photoelectric conversion layer is composed of a lower electrode layer. As a supplementary explanation, various processing steps such as photolithography and etching are performed as the edge surface of the photoelectric conversion layer is left exposed. It means that the edge surface of the photoelectric conversion layer is contaminated with resist material, metal material of the lower electrode and impurities including those materials. Such a matter has caused a problem that the contamination can make an electrical leakage path between both electrodes of a photodiode and the dark current increases. Further, a protecting film is formed for the patterned photoelectric conversion layer, which results in embedment of the cause of leakage.
In view of that, JP-A No. 2010-067762 discloses a method to perform a cleaning treatment by hydrogen plasma on the contaminated edge surface of the photoelectric conversion layer before the protecting film is formed. Concretely, the upper electrode is formed of known light-shielding metal and there is provided a mask structure by forming a passivation layer on an ITO upper electrode because the cleaning treatment can deoxidize the upper electrode under the condition that the upper electrode is a conductive oxide film such as an ITO (Indium Tin Oxide) film.
However, in the prior arts, the above method can make deterioration of the aperture characteristics of a photodiode and make the manufacturing steps complicated. Further, the above method just provides a solution to remedy the contaminated condition by a cleaning treatment, and it can be considered that the contamination is not removed completely through the method. JP-A No. 2004-063660 discloses a method to process the lower electrode by patterning before the photoelectric conversion layer is formed. This method actually provides an effect that a leakage path is not created but does not solve the problem about the layer separation as described above. In other words, JP-A No. 2004-063660 discloses a technology which works on two problems of “layer separation” and “countermeasures against electric leakage” which are incompatible problems in prior arts, but does not completely solve the both problems.
In order to achieve a photodiode with high sensitivity, enhancement of the S/N ratio is essential and the dark current is required to be reduced sufficiently, as described above. Further, needless to say, manufacturing the device without layer separation is a fundamental premise. As described above, “a structure which causes no layer separation” and “a structure which causes no electric leakage path” can be separately realized but are incompatible to be realized simultaneously in the prior arts, which has been confirmed by the inventor.
Therefore, realizing both of the structures at the same time is a problem to be solved, but it is not preferable that this realization makes a secondary problem such as an increase of manufacturing cost and deterioration of the opening aperture or the fill factor. The present invention seeks to solve the problem.